The invention relates to a seal for a shaft which, in regular operation, rotates in a first direction of rotation and passes through a wall which separates a higher pressure chamber from a lower pressure chamber, the seal including at least one seal component group which performs the sealing function in the first direction of rotation. Each one of these seal component groups includes, on the one hand, a first sealing member supported radially and in at least one axial direction at the shaft or at a component fixed thereto and connected with the shaft or the component by way of a first torque transmitting device while being sealed against the shaft by means of a first auxiliary seal arrangement. On the other hand, the seal component group includes a second sealing member supported radially and in at least one axial direction at the wall or at a component fixed thereto and connected with the wall or the component by way of a second torque transmitting device while being sealed against the wall or the component by means of a second auxiliary sealing arrangement. Both sealing members lie adjacent one another, either directly or separated by a thin layer of medium, at a sealing gap which receives the relative rotational movements.
Shafts which, in regular operation, rotate in only one predetermined direction, may take up the opposite direction of rotation under special operating conditions. One example for this is compressors which are always driven in one direction of rotation by a motor. If the motor is turned off and the compressor is charged with pressure on its low-pressure side, the compressor becomes a motor which drives the shaft in a direction opposite to its regular direction of rotation. The revolutions of the shaft in this opposite direction of rotation, even if they last only a relatively short time and/or do not occur at the same rate as in the regular direction of rotation, may lead to damaging consequences for the shaft seal due to increased wear on the slide seal faces or the furthering of leakages in an undesirable direction.
Gas lubricated slide ring seals are exposed to the danger of destruction to a particular degree after even a short-term reversal of the direction of rotation. Such slide ring seals are provided with conveying grooves in one of their two slide seal faces. Such grooves start from the higher-pressure chamber and pumping gas between the slide seal faces during rotation of the shaft in the first regular direction of rotation so that a gas pressure cushion is built up which separates the slide seal faces. In the opposite direction of rotation, these conveying grooves pull the gaseous medium out of the region of the sealing gap or are at least unable to build up gas pressure cushions. This results in direct contact between the slide ring faces, thus greatly increasing friction and destroying the sliding faces in the shortest time. Although attempts have been made to permit the establishment of pressure cushions in both directions of rotation by special selection of the groove shape and particularly a symmetrical configuration of the grooves relative to a radius placed through the axis of rotation, gas lubricated slide ring seals having such conveying grooves do not permit the establishment of sufficient gas pressure cushions in operation in the regular direction of rotation and have too high a leakage rate in regular operation.